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Purpose: Optical monitoring systems have gained substantial attention in modern radiotherapy, specifically in the context of Surface Guided Radiation Therapy (SGRT) which offers real-time patient surface monitoring, ensuring accurate and effective radiotherapy treatments. The aim of this paper is to evaluate the camera sensitivity towards different skin tones, categorized according to the Fitzpatrick scale, a universal classification of human skin tones, using a phantom.
Methods and Material: The study utilized Catalyst and SentinelTM systems (C-Rad, Uppsala, Sweden). The Alderson RANDO Female Pelvis phantom, located at isocenter in CT simulation and treatment rooms, served as experimental subject. Eighteen skin tone matching cotton cloths, selected based on Von Luschan’s chromatic and Fitzpatrick scales, were wrapped around the phantom for sensitivity evaluation. Camera sensitivity were optimized by adjusting threshold/gain (100-600%) and integration time during individual scans in both rooms. Temporal response analysis spanned two months, with sixteen measurements for each OSMS taken in varying light conditions.
Results: The Catalyst systems successfully detected the surface of cloth-covered phantoms with varying mean (standard deviation) integration times: 550(34) to 950(43) µs for Sentinel system and 2300(71) to 12000(400) µs for Catalyst system. The sensitivity parameters differed for each skin tone, with lighter skin requiring shorter integration times and gain/threshold values. Darker skin tones necessitated higher parameters for optimal surface images. The reliability of the systems declined with excessive parameters, leading to noise and compromised accuracy in patient positioning.
Conclusions: Optimized sensitivity parameters tailored to individual skin tones is crucial for effective real-time patient surface monitoring in radiation therapy, as variations in skin colour can affect the accuracy of measurements. The precession of skin colour measurements in Catalyst relies on carefully adjusting camera sensitivity parameters. However, careful consideration is essential, as excessive parameters are required for darker skin tones, compromising reliability. This suggests the need for exploring alternative SGRT image guidance methods for patients with darker skin tones.